1. Field of Invention
The invention relates to a thin-film transistor (TFT) and, in particular, to a TFT with body contacts for low-temperature polysilicon (LTPS) TFT LCD's.
2. Related Art
The thin-film transistor (TFT) is an important element in TFT liquid crystal displays (LCD's). The TFT technology is mainly divided into two types: one for amorphous silicon and the other for polysilicon. The technology for amorphous silicon is mature and thus the main products of LCD's. The technology for polysilicon requires recrystallization from the amorphous silicon to form polysilicon. In consideration of production costs and display quality, the low-temperature polysilicon technology is the main point of current developments. The electron mobility in polysilicon transistors is hundreds times faster than amorphous silicon ones. Thus, the polysilicon transistors have the advantages of a fast reaction speed, high brightness and high resolution for the display screen. Due to the fast electron mobility, the peripheral driving circuits can be integrated onto the polysilicon glass substrate to reduce the weight.
However, the current fabrication process of integrating the TFT and its driving circuit onto a polysilicon glass substrate has the drawbacks of a higher threshold voltage and a smaller mobility in comparison with that for complementary metal-oxide semiconductor (CMOS). It is thus seen that the driving current produced by the TFT is still smaller than that produced by the CMOS devices for the same size. As the TFT LCD has larger sizes and higher resolutions, more efficient TFT driving circuit are required. At the same time, the driving circuit area on the polysilicon glass substrate is limited by the pixel span. How to make highly efficient TFT devices within limited area has become an important topic currently under study.